I've done a bit of research here, but I still have some questions.
To start with, for anyone who isn't familiar with this, we can't say the brucha for lulav & etrog after completing the mitzvah, and the mitzvah is completed as soon as we gather the 4 species together and they are all right-side up, so we first pick up the Etrog upside-down, say the brucha and then turn it right-side up.
For the Etrog, The Shulchan Aruch says right-side-up is the way it grows: pitom-up, (and we should first pick it up pitom-down). And I remember being taught as a kid the Etrog first grows pitom-up and then turns pitom-down.
On the other hand,"The Second Jewish Book of Why" (page 266-267) says, etrogs grow pitom-down and growing pitom-up is a misconception that dates back to "the German Authority Jacob ben Moses Mollin (1360-1427)" who described the procedure in "Minhagay Maharil", and that it is an error in the Shulchan Aruch as well. It also cites that Rabbi Yechiel Epstein and Rabbi Israel Ben Meir Hakohen were aware that Etrogs grew pitom-down, but ruled it is a minhag (custom) now.
However, when I look at photos of etrogs, the young etrog-buds do grow pitom-up first:
As opposed to how a kiwi immediately hangs down:
Do Rabbi Yechiel Epstein (Aruch ha-Shulchan) and Rabbi Israel Ben Meir Hakohen (the Chafetz Chaim?) actually agree they don't grow this way?
Does it matter at what growth-point the etrog is considered a fruit (unripe fruits are ha'adama, not ha'eitz)? or what growth-point is an etrog kosher for use? Can an etrog be too small?
Are there other cases where we need to know the orientation of a fruit? -note: Willow branches grow facing down but we consider the "top" of the branch to be the the end of branch pointing towards the ground. Do we consider willow branches to also grow upwards first?